Repowering steam plant through addition of gas turbine and method for remodeling plant facilities

ABSTRACT

A repowering steam plant through the addition of a gas turbine, and a method for remodeling the plant facilities. This repowering steam plant is constructed by, to existing steam turbine facilities, additionally installing: gas turbine facilities; a high-temperature and high-pressure water line that is provided so as to branch off from a feedwater line in the steam turbine facilities and to pass through a boiler; a branch fuel line branched off from a fuel line in the steam turbine facilities; a reformer that reforms boiler fuel from the branch fuel line by high-temperature and high-pressure water from the high-temperature and high-pressure water line; and a reformed fuel line that supplies the fuel reformed by the reformer, as gas turbine fuel, to a combustor in the gas turbine facilities.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a repowering steam plant through theaddition of a gas turbine, constructed by remodeling an existing thermalpower plant, and to a method for remodeling the plant facilities.

2. Description of the Related Art

In comparison with a new and powerful power generating plant, an agingpower generating plant is low in the power generating efficiency andhigh in the fuel cost, and in addition, its NOx removal system forexhaust gas must be upgraded in order to meet an environmentalregulation value, so that its power generation cost becomes high. Insuch circumstances, a demand for a thermal power plant having higherefficiency is growing, with the deregulation of power supply and theintensification of environmental regulation as a background.

With this being the situation, in recent years, an attempt has been madeto repower a thermal power plant that is in a nonoperating status due toaging as described above, to implement a repowering steam plant, byadditionally installing gas turbine facilities thereto. In thisrepowering steam plant, the addition of the gas turbine allows exhaustgas to be reused as combustion air for a boiler, and enables the powergeneration capacity and energy efficiency to be enhanced. On the otherhand, heavy oil is generally used as fuel for a boiler in many cases,but it contains much vanadium and the like, which are responsible forhigh-temperature corrosion, and hence, it is undesirable for the heavyoil to be employed as fuel for a gas turbine, made of metal.Accordingly, reformers have been proposed that reform heavy oil into onethat can also be used as gas turbine fuel, using supercritical water(see, for example, JP, A 2002-129174).

SUMMARY OF THE INVENTION

Even if gas turbine facilities are additionally installed to an existingthermal power plant such as steam turbine facilities, the boiler fuelcontaining vanadium and the like, cannot be used as fuel for a gasturbine, and hence, a fuel line for the gas turbine facilities mustgenerally be provided in a separated manner. One possible measure to betaken here is to reform fuel for a boiler into fuel for a gas turbine byutilizing the above-described conventional art, and to thereby share thefuel line between the existing facilities and the gas turbinefacilities. In this case, however, facilities for refining supercriticalwater are required. Furthermore, with the gas turbine facilitiesinstalled, an NOx removal system for removing NOx in exhaust gas in thegas turbine facilities is required, with the protection of theenvironment in view.

Accordingly, it is an object of the present invention to provide arepowering steam plant through the addition of a gas turbine, therepowering steam plant allowing the cut-down of power generation cost byrepowering an existing thermal power plant through a minimum remodelingand by using reformed fuel as gas turbine fuel, and a method forremodeling the plant facilities.

To achieve the above-described object, the present inventionadditionally installs gas turbine facilities and a reformer forreforming fuel for existing facilities, to an existing thermal powerplant, and further, refines high-temperature and high-pressure water forfuel reformation, by utilizing the existing facilities.

According to the present invention, it is possible to reduce the powergeneration cost by repowering the existing thermal power plant through aminimum remodeling, and by using reformed fuel as gas turbine fuel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a repowering steam plant through theaddition of a gas turbine, according to an embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a repowering steam plant through the addition of a gasturbine, and a method for remodeling the plant facilities, according toan embodiment of the present invention will be described with referenceto the accompanying drawings.

FIG. 1 shows an the repowering steam plant according to this embodiment.

In FIG. 1, a portion surrounded by a chain line shows existing steamturbine facilities that are, for example, in a nonoperating status dueto aging. Broadly speaking, the steam turbine facilities 100 are adaptedto rotationally drive a steam turbine 2 by steam generated by a boiler1, and generate electric power by rotating a generator 3 using arotational power of the steam turbine 2.

Here, description of the steam turbine facilities 100 will be provided.First, a fuel line 4 for supplying fuel from fuel feeding facilities(not shown) is connected to the boiler 1, while a feedwater line 5 forsupplying make-up water from a water source (not shown) is connected tothe steam turbine 2 through the boiler 1. Fuel to be supplied to thefuel line 4 is freed in advance from sodium, potassium, and the like,which are responsible for high-temperature corrosion, by a salt removalsystem (not shown).

Connected to the feedwater line 5, is a condensate line 6 that, afterrecovering steam having worked in the steam turbine 2, circulates thesteam in the feedwater line 5. The boiler 1 combusts fuel supplied fromthe fuel line 4, and supplies water discharged by a feedwater pump 7provided midway through the feedwater line 5, to the steam turbine 2, ashigh-temperature and high-pressure steam. This causes the powergenerator 3 rotating in conjunction with the steam turbine 2 to generateelectric power. The steam having rotationally driven the steam turbine 2is condensed by a condenser 8 provided midway through the condensateline 6, and returned to the feedwater line 5.

The repowering steam plant according to this embodiment is constructedby remodeling such existing steam turbine facilities 100 as follows:First, gas turbine facilities 200 and a reformer 300 for fuel are newlyinstalled to the existing steam turbine facilities 100. Then, to thesefacilities, a high-temperature and high-pressure water line 10 branchedoff from the existing feedwater line 5 is added. Next, a branch fuelline 11 branched off from the existing fuel line 4 is added thereto, andfurther, a branch steam line 13 branched off from the inlet of theexisting steam turbine 2 is added thereto. When constructing thisrepowering steam plant, each portion thereof is configured as describedbelow.

Connected to the reformer 300, are the high-temperature andhigh-pressure water line 10 branched off from an upstream portion of theboiler 1 in the feedwater line 5, and the branch fuel line 11 branchedoff from the fuel line 4. Out of these, the high-temperature andhigh-pressure water line 10 is provided so as to pass through the boiler1. This high-temperature and high-pressure water line 10 may be branchedoff from the condensate line 6 instead of the feedwater line 5. Also,the branch fuel line 11 has a pump 12. Furthermore, the presentrepowering steam plant includes a branch steam line 13 branched off fromthe steam line (downstream portion of the boiler 1 in the feedwater line5), which supplies steam to the steam turbine 2; and a heat exchanger 14for exchanging heat between the branch steam line 13 and the branch fuelline 11.

The reformer 300 and a combustor 15 in the gas turbine facilities 200are connected by a reformed fuel line 16. As described above, boilerfuel from the branch fuel line 11 is reformed by decomposing andremoving vanadium and the like contained therein, using high-temperatureand high-pressure water from the high-temperature and high-pressurewater line 10, and thereafter supplied to the combustor 15 by thereformed fuel line 16. The vanadium having been decomposed and removedfrom the boiler fuel by the reformer 300 is discharged from the reformer300 together with water through a drain line 17.

Within the gas turbine facilities 200, in the combustor 15, combustiongas is refined by combusting reformed fuel from the reformed fuel line16 together with compressed air for combustion from a gas turbinecompressor 18, and this combustion gas rotationally drives the gasturbine 19. A power generator 20 is connected to the gas turbine 19, andgenerates electric power by rotating together with the gas turbine 19.The gas turbine 19 may be of either a uniaxial type or biaxial type.

The gas turbine 19 and the boiler 1 are connected by a combustion gasline 21, and combustion gas (exhaust gas) from the gas turbinefacilities 200 is introduced into the boiler 1, as combustion air.

By remodeling the existing steam turbine facilities 100 as describedabove, a repowering steam plant after the remodeling operates asfollows:

First, one portion of fuel supplied to the boiler 1 is subjected to apressure up to a predetermined pressure. Thereafter, in the course ofpassing through the branch fuel line 11, the portion of the fuel issubjected to a heat exchange with steam passing through the branch steamline 13 by the heat exchanger 14, and supplied to the reformer 300 afterundergoing a temperature up.

On the other hand, steam exiting the steam turbine 2 is introduced intothe condenser 8, and after being condensed there, it is returned to thefeedwater line 5 through the condensate line 6. Then, together withmake-up water from the water source (not shown), the condensate issubjected to a pressure up to a set pressure by the feedwater pump 7 forthe boiler, and after undergoing a temperature up to a set temperatureby passing through the boiler 1, it is supplied to the reformer 300, ashigh-temperature and high-pressure water.

Here, it is preferable that the “set pressure” be in a pressure range onthe order of, e.g., 10 MPa to 25 MPa, and that the “set temperature” bein a temperature range on the order of, e.g., 400° C. to 470° C., whichranges allow states including a subcritical state and a supercriticalstate to be provided. The foregoing high-temperature and high-pressurewater, therefore, is assumed to include subcritical water, supercriticalwater, and water in temperature and pressure states close to those ofthe subcritical or supercritical water.

Here, “supercritical fluids” refer to fluids that are in a state beyondthe critical temperature and pressure (critical points) in which gas andliquid can coexist, and that have characteristics exhibiting both of theliquid-like behavior to dissolve solutes and gaseous behavior superiorin the diffusing capability. Among them, particularly, the supercriticalwater is water that has been subjected to a temperature up and apressure up above its critical points (generally, 22 MPa and 374° C.).The supercritical water exerts a large effect as a reaction solvent andhas an advantage of being capable of continuously controlling variousproperties of a fluid by the variation in pressure and temperature, thusproviding applicability to various reaction systems. The supercriticalwater is capable of dissolving any organic substance, and generally, candissolve even dioxin, polychlorinated biphenyl (PCB), and the like up tonearly 100% of them.

The boiler fuel supplied to the reformer 300 is reformed by vanadium andthe like being decomposed and removed by an action of thehigh-temperature and high-pressure water, serving as a reaction solvent.The reformed fuel is supplied to the combustor 15 in the gas turbinefacilities 200 through the reformed fuel line 16, and the vanadium andthe like that have been decomposed and removed are discharged out of theline through the drain line 17.

The fuel supplied to the combustor 15 is mixed with combustion air thathas been subjected to a pressure up by the gas turbine compressor 18,and combusts. The resultant combustion gas at a high-temperature and ahigh-pressure drives the gas turbine 19. The power generator 20 isdriven by a rotational power of the gas turbine 19, thereby generatingelectric power.

The combustion gas (exhaust gas) having worked in the gas turbine 20 isusually high-temperature air of which the temperature in the vicinity ofthe outlet of the gas turbine 20 is on the order of 600° C. Thiscombustion gas, therefore, is supplied to the boiler 1 through thecombustion gas line 21, and employed as combustion air for the boiler 1,whereby thermal energy of the exhaust gas is effectively utilized. Inthis case, if oxygen concentration in the exhaust gas is insufficient,outside air may be taken in as necessary. Although the temperature ofthe exhaust gas in the gas turbine facilities 200 is high, it is nothigh enough to produce steam at high-temperature and high-pressurenecessary to drive the steam turbine 2. This being the situation, theexhaust gas supplied to the boiler 1 is used as combustion air, asdescribed above, and high-temperature and high-pressure steam obtainedby supplying fuel to the boiler 1 and re-combusting it, is supplied tothe steam turbine 2, whereby the rotational power of the steam drivesthe power generator 3 to generate electric power.

Among conventional aging thermal power plants like the steam turbinefacilities 100 shown in FIG. 1, there are many plants that are in anonoperating status due to low power generating efficiency and highpower generating cost. In some of these plants, the above-describedrepowering by the remodeling into a repowering steam plant is performedfor the purpose of enhancing power generating efficiency and output. Inthis case, although fuel containing much heavy metals such as vanadiumand the like can be used as fuel for the boiler, it cannot be used asfuel for the gas turbine, which is a high-speed rotating body, if thefuel is left uncontrolled. This is because the vanadium in the fuel ishigh in the concentration and responsible for failure of equipment dueto high-temperature corrosion. Therefore, when remodeling theconventional thermal power plant into a repowering steam plant by newlyadding gas turbine facilities, facilities for reforming the fuel linefor the steam turbine facilities, or the fuel for the boiler into fuelfor the gas turbine facilities is required.

For supplying condensate from the steam turbine to the boiler facilitiesgenerating high-temperature and high-pressure steam, the steam turbineplant typically has facilities for pressuring up condensate. Therefore,when constructing a repowering steam plant by remodeling the steamturbine facilities, the aforementioned facilities for pressuring upcondensate can also be utilized as facilities for refininghigh-temperature and high-pressure water, which is a reaction solventnecessary to reform the boiler fuel into the gas turbine fuel.

With such being the situation, in the present embodiment, as describedabove, there is provided a high-temperature and high-pressure water line10 for supplying high-temperature and high-pressure water for fuelreformation, making use of the existing boiler feedwater pump 7 andboiler 1, and the boiler fuel is partly reformed using high-temperatureand high-pressure water from the high-temperature and high-pressurewater line 10, whereby the resultant fuel is supplied as fuel for thenewly installed gas turbine facilities 200. In this way, making thereformed fuel refinable by making the most of the existing facilities,allows the fuel facilities to be shared between the existing facilitiesand the added facilities. Also, the required amount of high-temperatureand high-pressure water used for the reformation of fuel into the gasturbine fuel is very slight as compared with the amount of feedwater tothe steam turbine, so that the remodeling range of facilities can bereduced to a minimum when remodeling the existing conventional thermalpower plant.

The use of the high-temperature and high-pressure water allows theamount of vanadium contained in the boiler fuel to be reduced to theallowable value or less by means of the reformer 300, thereby enablingthe fuel to be used as gas turbine fuel. It is therefore possible toemploy heavy oil C, generally used as boiler fuel and inexpensivecompared with heavy oil A, generally used as gas turbine oil. Thisenables a significant cut-down of the fuel cost, leading to asignificant reduction in the power generating cost.

Furthermore, in the present embodiment, the provision of the branchsteam line 13 and the heat exchanger 14 allows the heat of steamsupplied to the steam turbine 2 to be used to enhance the temperature offuel to be reformed, thus enabling the thermal energy in the system tobe effectively utilized.

In addition, for example, when oil is used as fuel, the gas turbinefacilities 200 require an NOx removal system for removing NOx in exhaustgas therein for the purpose of meeting the environmental regulationvalue. In this respect, in this embodiment, the exhaust gas from the gasturbine facilities 200 is introduced into the existing boiler 1 throughthe combustion gas line 21 to re-combust it, thereby allowing the NOxremoval system of the boiler 1 to be shared between the boiler 1 and thegas turbine facilities 200 without the need to newly install an NOxremoval system for the gas turbine facilities 200. This can alsocontribute toward reducing the remodeling range of the existing plant toa minimum.

1. A repowering steam plant through the addition of a gas turbine, therepowering steam plant comprising: existing steam turbine facilitiesthat rotationally drive a steam turbine using steam generated by aboiler; gas turbine facilities additionally installed to the existingsteam turbine facilities; a high-temperature and high-pressure waterline that is provided so as to branch off from a feedwater line or acondensate line in the steam turbine facilities and to pass through theboiler; a branch fuel line branched off from a fuel line in the steamturbine facilities; a reformer that reforms boiler fuel from the branchfuel line by high-temperature and high-pressure water from thehigh-temperature and high-pressure water line; and a reformed fuel linethat supplies the fuel reformed by the reformer, as gas turbine fuel, toa combustor in the gas turbine facilities.
 2. The repowering steam plantaccording to claim 1, further comprising a combustion gas line thatintroduces combustion gas from the gas turbine facilities, as air forcombustion, into the boiler.
 3. The repowering steam plant according toclaim 1, further comprising a branch steam line branched off from thesteam line for supplying steam to the steam turbine, and a heatexchanger exchanging heat between the branch steam line and the branchfuel line.
 4. The repowering steam plant according to claim 1, whereinthe pressure of the high-temperature and high-pressure water is on theorder of 10 MPa to 25 MPa, and the temperature thereof is on the orderof 400° C. to 470° C.
 5. A method for remodeling plant facilities, themethod comprising the steps of: providing a reformer for reforming fuelfor the boiler to existing steam turbine facilities, when constructing arepowering steam plant by additionally installing gas turbine facilitiesto the existing steam turbine facilities that rotationally drives thesteam turbine using steam generated by the boiler; connecting, to thereformer, a high-temperature and high-pressure water line that isprovided so as to branch off from a feedwater line or a condensate linein the steam turbine facilities and to pass through the boiler, and abranch fuel line branched off from a fuel line in the steam turbinefacilities; and connecting the reformer and a combustor in the gasturbine facilities by a reformed fuel line, and causing the boiler fuelfrom the branch fuel line, to be reformed by high-temperature andhigh-pressure water from the high-temperature and high-pressure waterline, and to be supplied to the combustor in the gas turbine facilitiesthrough the reformed fuel line.